A fuel injection pump for diesel engines includes a governor, which adjusts the amount of fuel injection by rotating a plunger and adjusting the opening time of a plunger lead. For constituting the governor, a linearly movable control member directly engages with a control sleeve which is rotatable integrally with the plunger, and an actuator for moving the control member is connected to the control member by a governor link. For serving as the control member, there are a control rack meshing with a pinion provided on the control sleeve, a control slider whose fork arm pinches a lock pin provided on the control sleeve, and so on. For serving as the actuator for moving the control member, if the governor is a centrifugally operated governor, there is a governor sleeve which is moved with the centrifugal force of a camshaft, for example. If the governor is an electronic governor, for example, an electromagnetic solenoid may serve as the actuator.
Since a governor mechanism part including a governor weight and the governor sleeve etc. in the case of the centrifugally operated governor, or an electromagnetic solenoid part in the case of the electronic governor is large-scale, it is offset from a pump mechanism part equipped with a plunger, a delivery valve, etc. On the other hand, the above-mentioned link must engage with the control member in the pump mechanism part. Therefore, when attaching the plunger to the pump mechanism part, the governor link needs to be inserted together with the plunger into the pump mechanism and engaged to the control member while being finely tuned in its positioning, thereby complicating assembly operation of the pump mechanism part itself. Suppose that the governor link previously included in the governor mechanism part is automatically made to engage with the control member in the pump mechanism part during the assembling for combination of the governor mechanism part with the pump mechanism part incorporating the plunger etc. In this case, the assembly of a fuel injection pump becomes very easy. However, there is no conventional fuel injection pump of such a configuration.
Moreover, an end of the camshaft of a fuel injection pump is projected outside from a bearing of pump housing, and provided thereon with a key such as a woodruff key through which a reduction gear is fixedly provided thereon so as to be interlockingly connected to a crankshaft in a crankcase. If the bearing allows the key to pass therethrough, in the insertion process of the camshaft to the pump housing, this key can be provided only by passing the camshaft previously loaded with the key through the bearing to project the outer end of this camshaft outward. However, if the camshaft is loaded with a key in a conventional manner, the distance between the axis of the camshaft and a part of the key that is radially farthest from the axis of the camshaft will become larger than the radius of inner periphery of the bearing. Therefore, it becomes inevitable that the key is loaded on the projection end of the camshaft after the camshaft is passed through the pump housing and projected at its outer end outward from the pump housing. Furthermore, for removing the camshaft from the pump housing, not only the gear but also the key must be removed from the pump shaft so as to allow the projection end of the camshaft to pass the bearing.
Next, the problem of the conventional diesel engine will be explained in relation to the injection time of a fuel injection pump. In a diesel engine, the fuel pressurized by hundreds atmospheric pressure with the fuel injection pump is injected into a combustion chamber from a nozzle of a fuel injection valve attached to a cylinder head at about 20 degrees prior to the top dead center of the crankshaft in its rotational angle (in lead zone of crank angle).
Since combustion is performed in the integrity that air is superfluous, there is little concentration of CO and HC in exhaust gas of a diesel engine far compared with that of a gasoline engine. However, a diesel engine exhausts much NOx. Reduction of exhaustion of NOx is the most important problem for diesel engines.
NOx is generated when nitrogen and oxygen are heated to combine with each other. Therefore, generally, the better combustion is, the more NOx is exhausted. That is, the abundance of NOx increases, so that the combustion temperature is high and the duration of combustion is long. Furthermore, when the mixture ratio of air and a fuel is a certain value, this abundance reaches maximum.
In order to reduce NOx under exhaust gas, it is possible to adopt EGR system or a crankcase emission control system besides improvement of the combustion chamber in an engine, or improvement of an air intake-and-exhaust system. However, if EGR system is performed, the soot under exhaust gas will mix in lube through inhalation air, and early degradation of lube and wear of an engine sliding part will pose a problem. Moreover, when it is equipped with a crankcase emission control system, soot accumulates on the lube adhering to the wall in an intake manifold so as to choke the intake manifold, thereby reducing an engine performance.
As another reduction method of NOx, it is improvement of an injection system, especially a fuel injection pump so as to delay the start time of fuel injection. However, this leads to aggravation of combustion so as to decline the output force and thermal efficiency, increase CO or HC, aggravate the engine starting at low-temperature, and increase black smoke concentration, etc. Therefore, when an engine starts or high load is applied on the engine, priority should be given over advancing of fuel injection starting time for efficient combustion to reduction of NOx under exhaust gas. Thus, since the required time of a fuel injection start changes with engine operation situations, it becomes important how fuel injection start time is controllable so as to agree with conflicted required times.
Such control of fuel-injection time is well known by JP6-50237A. According to this document, a sub lead other than an original plunger lead (main lead) is formed in the head of a plunger. Corresponding to this sub lead, a leak port which is open for free passage to a fuel escaping circuit is formed in a plunger barrel. By bringing the sub lead into communication with the leak port, the fuel in a fuel-compression chamber is made to escape in early stages of the fuel-discharging stroke of the plunger so as to delay the fuel-injection time substantially.
In the cited plunger, when the rotational location of the plunger by the governor goes within a fixed range (for example, a range corresponding to the time of an engine start, or if the plunger is controlled by an electronic governor, a range corresponding to the time when the engine is high-loaded), the sub lead is located apart from the leak port so as to be shut off from the leak port so that the plunger starts discharging fuel of the predetermined pressure to the delivery valve shortly after it closes the inhalation port to finalize the fuel-inhaling stroke thereof. Whereby, the fuel-injection time can be advanced.
However, in the case of this cited example, strict accuracy is required in processing of the sub lead, the leak port and the like as well as positioning of the plunger. When an error is in these process tolerances, the fuel-injection start time does not correspond well to the control of fuel oil consumption based on engine operation situations. In this regard, if the amount of fuel escaping from each leak port is not unified exactly, the engine performance varies among fuel injection pumps. Particularly, it comes to be considered that a train type fuel injection pump or the like has a plurality of plungers whose injection characteristics are different from one another so as to cause variation of combustion ability among the cylinders of an engine. On the other hand, the amount of leaking fuel may be requested to increase or decrease according to variation of engines. Neither the dissolution of the variation in the engine performance by such process error nor adjusting of the amount of fuel leaks as occasion demands is attained depending on the above-mentioned reference technique.